1. Field of the Invention
The present invention relates to a tape automated bonding process for fabrication of packaged integrated circuit semiconductor devices or IC dies and to lead frame and package constructions resultant from such processes.
2. Prior Art
Semiconductor chips or integrated circuit (IC) dies have multiple electrical contact pads which are connected through external electrical leads or thin film conductors to plug-in contacts or bonded to other members on a printed circuit board or the like. In production processes, tape automated bonding (TAB) has been employed where a strip of metal tape in reel form provides a plurality of groups of metallic parts where each group includes interconnected finger contacts. These are connected at inner beam ends to die contact pads by bonding wires, compression bonding, or other means. The outer ends of finger contacts form the plug-in contacts or other connectible contacts of the die package.
This technique is typified by the method and construction shown in U.S. Pat. No. 3,611,061 where a continuous metal tape has arrays of duplicate metal pathways forming narrow parallel finger contacts extending from a die-connect end to an integral metal transverse stabilizer for which holds the frame while the IC die is being bonded and encapsulated. The somewhat flexible metal tape, which is of a thickness from about 2.3 to 2.9 mils, has interconnect links between the finger contacts and sprocket hole perforations on the outer edges for indexing and moving the tape through fabrication stations. After the die, inner ends and the die-to-ends bonds are encapsulated the links are sheared and the stabilizer bar and outer tape edges trimmed off resulting in a typical DIP (dual-in-line) or other package with finger-type plug-in leads extending from each side of the package. The device is then ready for testing.
U.S. Pat. No. 3,689,991 shows a two-layer tape wherein sets of finger-like leads are secured or formed by etching techniques on an insulative tape. These leads are essentially thin copper foils with a thickness of from about 1.0 to 1.6 mils. Such insulative tape affords support for the thin leads during the die bonding and encapsulation process and partly remains part of the internal final assembly. Three-layer tape has also been employed which is similar to the two-layer tape described above except that the thin copper foil is laminated typically to a polymide layer previously coated with an adhesive material. It has been known to test two-layer and three-layer encapsulated packages prior to their complete trimming from the tape. This has been possible since the film is originally supported and continues to be supported in the fabrication process by the insulative layer. U.S. Pat. No. 3,444,440 also shows a metal lead frame for mounting an IC die albeit not in reel form. After die bonding and encapsulation, the "picture-frame " edges (FIGS. 5-8) are trimmed off and the final package is ready for test. U.S. Pat. No. 4,234,666 shows TAB processing of thin, delicate copper foil including inner and outer gang bonding of the leads to the die and lead frame, respectively.
Honeywell Corporation has utilized a two-layer polyimide/ copper tape in which an array of contact fingers and die attach area are mounted into a prefabricated stiff plastic frame akin to a 35 mm film negative holder and the die bonded to inner contact fingers. The die and the bonds are then tested after blanking of interconnects but before encapsulation of the die and the bonds.